Studies in the Osteopathic
The Nerve Centers: Volume
Louisa Burns, M.S., D.O., D.Sc.O.
THE NUTRITION OF THE NERVOUS SYSTEM
Neurons are nourished by the lymph which bathes them, and the lymph is
derived from the blood circulating through the vessels. The central
nervous system and the sensory and sympathetic ganglia are alike in the
lack of lymphatic vessels. In every case, in mammals, the nerve cell
lies surrounded by a pericellular lymph space, and it is thus bathed on
every side by the nutrient lymph.
arterial supply of the cord is very plentiful. The two posterior
spinal arteries and the anterior spinal artery extend through the length
of the cord, and receive with each nerve root branches from the cervical,
lumbar or intercostal arteries. The anastomosis of these arteries
is complex and efficient. It is not conceivable that any vertebral
lesion short of actual crushing could bring about a diminution of the arterial
supply to the cord through direct pressure. The effects upon the
spinal circulation indirectly produced through vaso-motor impulses may
be discussed at a later time.
these longitudinal arteries and their anastomotic branches arise the arteries
which enter the cord. These smaller arteries are of two classes,
centripetal and centrifugal. Both sets are composed of terminal arteries,
thus no anastomosis is found within the cord; there is, however, a certain
amount of overlapping of the areas of distribution of the vessels.
centrifugal arteries arise chiefly from the anterior artery. The
branches enter the cord by way of the anterior fissure. They break
up into fine branches which supply the gray matter, for the most part,
though a few small branches supply the white matter in the immediate neighborhood
of the centrifugal system.
the posterior arteries arise a few branches of the centrifugal system also.
These enter the posterior median septum and are distributed to the posterior
white matter and to the central gray matter.
centripetal arteries arise from both the anterior and the posterior longitudinal
arteries. The branches from these pass around the cord, break up
into finer terminal branches, and enter the cord at right angles to its
surface. These finer terminals supply the white matter of the anterior
and lateral funiculi, and in part the posterior funiculi. The white
matter is less richly supplied with arteries than the gray.
double arterial supply presents no explanation. That some clinical
significance is attached to this vascular supply appears apparent when
one remembers the frequency with which lesions of the gray matter are found
without any apparent disturbance of the gray matter, and how often the
gray matter is diseased without there being any recognizable lesion of
the white matter. This clinical phenomenon may, of course, be interpreted
otherwise than by artery supply.
centrifugal and centripetal arteries are supplied with vaso-motor nerves,
which seem to be derived from the sympathetic ganglia of the same or adjoining
segments. It is not known whether the centrifugal and centripetal
arteries have identical vaso-motor innervation. It is very
evident that the disturbances which interfere with vaso-motor impulses
to the viscera, skin, etc., may also interfere with the vaso-motor impulses
to the corresponding spinal areas.
veins of the cord are very plentiful. The fissural veins drain the
areas of the centrifugal arteries, while the root veins and the smaller
veins emerging from the surfaces drain the areas supplied by the centripetal
arteries. All of these veins unite in forming the spinal venous plexus.
This plexus is made up of freely anastomosing veins. They have been
rather vaguely divided into six longitudinal veins, but the anastomosis
is so rich and the variations are so many that it is difficult to trace
them as exactly six through the extent of the cord. This venous plexus
is drained into the vertebral, lumbar, sacral, and intercostals veins.
The veins of the central nervous system, including the spinal cord, are
vessels of the medulla and pons resemble those of the cord. The vertebral
arteries unite to form the basilar. From the two vertebrals below
their union, from the basilar, and from the anterior and the posterior
spinal arteries the arteries of the medulla and pons are derived.
They may be divided into three sets. These sets are composed of terminal
arteries, though their areas of distribution overlap to a certain extent.
median arteries pass through the substance of the medulla and pons, and
divide into fine branches distributed to the nuclei of the cranial nerves.
The beginnings of the nerve roots also are partly supplied by the median
root arteries enter the medulla and pons with the nerve roots. They
include central and peripheral branches. The former are distributed
with the median arteries to the nuclei of the cranial nerves, the latter
are distributed to the white matter in the neighboring areas.
lateral medullary and pontine arteries pass around the external surface,
and are distributed to the olives, the restiform bodies, and the pyramids.
Branches from the inferior cerebellar arteries are distributed to the restiform
bodies and the formatio reticularis.
veins of the medulla and pons follow the arterial arrangement for the most
part, and are drained into the superior and inferior petrosal sinuses or
into the basilar plexus.
cerebellum is furnished by three arteries on each side. The superior
cerebellar is derived from the basilar. It is distributed to the
superior surface. A small portion of the posterior border escapes
from the supply of the superior cerebellar, which supplies also the geniculate
bodies, the quadrigeminates, the tela choroidea, a part of the third ventricle,
and sends some branches to the posterior surface of the pons.
are two inferior cerebellar arteries, the anterior and the posterior.
The anterior is from the basilar, also. It is distributed to the
inferior anterior aspect of the cerebellum and the anterior inferior border.
posterior inferior artery is given off from the vertebral artery before
it unites with its fellow to form the basilar. The posterior inferior
cerebellar artery supplies the medial part of the hemisphere, the inferior
part of the vermis; it communicates with the superior cerebellar artery
upon the posterior superior surface. There is a fairly free anatomosis
among the larger branches of the three cerebella arteries.
cerbellar veins are called by the same names as the arteries. The
internal cerebellar veins empty into the superior and inferior veins.
The superior veins empty into the great cerebral veins, for the most part,
but several smaller veins associated with these empty into the superior
inferior veins run upward into the transverse or straight sinus, or into
the inferior petrosal and occipital sinuses.
circulation through the brain presents many peculiarities. The vertebral
arteries unite to form the basilar, the basilar unites with the internal
carotids by way of the posterior communicating arteries, the anterior cerebral,
from the internal carotid passes forward, and the left is united with the
right by means of the anterior communicating artery. Thus a complete
circle is formed which surrounds the brain stem. From this arterial
circle (circle of Willis, in the old naming) the arteries are derived which
supply the brain, and this circle is practically the last anastomosis of
these arteries. There is a certain amount of overlapping in their
areas of distribution, but no anastomosis.
brain is supplied with blood by two distinct systems, the ganglionic system
and the cortical system. There is very little overlapping in the
areas of distribution of the two systems. Between them lies an area
of the brain which is poorly supplied with blood, and this area is subject
to the diseases of malnutirion in the aged or in those in whom any cause
of enfeebled cerebral circulation is found.
ganglionic arteries are small. They are distributed for the most
part in an efferent manner, and supply the base of the brain and the basal
include the antero-median and the postero-median, the right and left antero-lateral
and the right and left postero-lateral. Thus there are six chief
arteries which, with their branches, compose the ganglionic system.
antero-median is a branch of the anterior cerebral. It supplies the
region of the optic chiasma, the rostrum of the corpus callosum and the
head of the caudate nucleus.
antero-lateral arteries are derived from the middle cerebral. They
are distributed to the optic thalamus, the corpus striatum and the internal
capsule. One of the branches, the lenticulo-striae, is of interest
because of its liability to hemorrhage in elderly people or in those subject
to artero-sclerosis. It is called the “artery of cerebral hemorrhage”
for this reason. Since it supplies the striatum and the internal
capsule, the paralysis which results from this hemorrhage is very widespread
and is contra-lateral.
postero-lateral arteries are from the posterior cerebral. They supply
the posterior parts of the thalamus, the geniculates, the quadrigeminates,
and the pineal body. These areas overlap the area of distribution
of the superior cerebellar artery to a certain extent.
postero-median artery is derived fro the posterior cerebral and the posterior
communicating arteries. It supplies the medial parts of the thalamus
and the third ventricle, the cerebral peduncles and the space between
are two choroidal arteries, an anterior and a posterior. The anterior
arises from the internal carotid and follows the optic tract to the inferior
end of the choroidal fissure. It supplies the choroids plexus of
the inferior horn of the lateral ventricle, and gives collateral branches
to the optic tract and to the hippocampus and hippocampal gyrus, the dentate,
crus of the fornix, and posterior part of the internal capsule.
posterior choroidal include two or more arteries on each side. These
arise from the posterior cerebral and they pass forward in the transverse
and choroidal fissues to be distributed to the choroid plexuses of the
third and lateral ventricles.
cortical arteries are those which supply the cortex of the hemispheres.
These arteries give off a few branches which supply the ganglionic system,
but after these few branches are lost no further relationship between the
two systems is evident. Not only is there no anastomosis between
the two systems, but there is almost no overlapping of their areas of distribution.
anterior cerebral artery arises from the internal carotid. It passes
forward toward the longitudinal fissure, and the right anterior cerebral
is joined to the left anterior cerebral by a very short anastomotic branch,
the anterior communicating artery. The antero-median ganglionic artery
arises from the anterior cerebral. There are four branches of the cortical
system from the anterior cerebral, the anterior, middle and posterior internal
frontal arteries, and the internal orbital artery. The anterior internal
frontal supplies the anterior part of the gyrus cinguli and superior frontal
gyrus on the medial aspect of the brain, and the superior and middle frontal
gyri on its outer aspect.
middle internal frontal artery supplies the middle part of the gyrus cinguli,
the paracentral lobule, the upper part of the superior frontal and the
precentral and postcentral gyri.
posterior internal frontal artery supplies the corpus callosum, the posterior
part of the gyrus cinguli, of the paracentral lobule, the precuneus, and
the superior parietal lobule.
internal orbital artery supplies orbital gyri, the optic chiasma, the olfactory
bulb, tract, the roots of the olfactory tract, and the parolfactory area.
four arteries are distributed to the cortical area as far posteriorly as
the occipito-parietal sulcus.
middle cerebral artery is the largest branch of the internal carotid, and
it receives the direct current of its blood stream. Since the left
internal carotid receives the most direct current of the blood stream from
the ascending aorta, the middle cerebral artery is more apt to receive
foreign substances carried in the blood stream than in any other artery
in the body. For this reason the area of distribution of the left
middle cerebral artery, and especially its ascending frontal branch, is
apt to suffer from embolism. Since this area includes the kinesthetic
area of the cortex, the embolus in this region results in a contra-lateral
middle cerebral artery (Sylvian artery) runs in the lateral fissure of
the cerebrum (Sylvian fissures). It gives off the antero-lateral
artery, and opposite the insula (Island of Reil) breaks up into six terminal
lateral orbital (inferior external frontal) is distributed to the anterior
and posterior orbital gyri and the inferior frontal gyrus).
ascending frontal includes two chief branches, which follow the central
sulcus (fissure of Rolando) as far as the precentral sulcus, then follows
this to supply the anterior central gyrus and a part of the middle frontal
ascending parietal is distributed to the posterior central gyrus (ascending
parietal convolution) and the neighboring superior and inferior parietal
parieto-temporal arteries include three chief branches. Two of these
are distributed to the superior, middle and the upper part of the inferior
temporal gyri. The posterior branch follows the posterior ramus of
the lateral cerebral fissure (fissure of Sylvius) to its termination.
It then divides into two branches, one of which passes upward to the supra-marginal,
post-parietal and angular gyri, while the other supplies the posterior
part of the temporal lobe.
right and left posterior cerebral arteries are formed by the division of
the basilar arteries. They are joined to the internal carotids by
the posterior communicating arteries. The posterior cerebral arteries
give off the postero-median and the postero-lateral ganglionic arteries,
and two or more posterior choroidal arteries. Its cortical branches
are three, the occipito-parietal, the calcarine, and the temporal.
occipito-parietal supplies the cuneate and lingual gyri, the lateral and
superior gyri of the occipital lobe.
temporal branches are three in number, the anterior, middle and posterior
temporal branches. These are distributed to the gyrus hippocampus,
the fusiform gyrus, and the inferior temporal gyrus.
arteries described lie upon the surface of the brain. From them arise
many very fine terminal arteries which penetrate the brain and are distributed
to its gray matter. These arteries do not penetrate very deeply into
the brain, and the white matter receives most of its comparatively scant
blood supply from the ganglionic system.
arteries of the brain are now known to receive vaso-motor nerves from the
sympathetic system. (Fig. 21.) The fibers arise as white rami
from the upper thoracic segments of the cord, and pass with the sympathetic
chain to the superior cervical ganglion. Here the medullated fibers
terminate by entering into the formation of the superior cervical pericellular
baskets. The axons of the sympathetic cells pass by way of the carotid
plexus to the arteries of their distribution.
neuroglia cells, called “podasteroids,” seem to be concerned in the nutrition
of the brain. These cells lie along the pericellular lymph spaces,
partly inclosing them, and partly supporting the blood vessels, especially
the capillaries. These podasteroids send prolongations to the walls
of the vessels, and rest upon them by a footlike expansion. (Figs.
22, 23.) Under certain abnormal conditions, such as hemorrhage, poisoning,
etc., the podasteroids are found to be swollen and the footlike expansions
are filled with debris, bits of blood clot, etc.
is, however, probable that the most efficient regulation of the cerebral
circulation is through changes in the general blood pressure. The
brain is inclosed in the dense skull, the brain itself is almost fluid,
the lymph and blood are fluids, and therefore the cranial contents are
practically noncompressible. Vaso-constriction or vaso-dilaton of
the cerebral vessels must, therefore, be less efficient in modifying the
cerebral circulation than are changes in the systemic blood pressure.
This is most efficiently modified by variations in the splanchnic circulation,
by variations in the heart beat, and by variations in the pulmonic blood
veins of the brain have several peculiarities. They have no valves.
They are enclosed in bony channels called sinuses. They are surrounded
by perivascular lymph spaces. They are very large in proportion to
the arteries whose blood they receive. They have very free anastomoses.
The veins empty at a recurrent angle. The veins of the skull have
many pouchlike diversions. Enissary veins through the skull assist
in preserving a constant intracranial pressure in the presence of variations
in the systemic pressure and of overfilling of the cerebral vessels.
sinuses are formed by folds of the dura mater. They are lined with
endothelium continuous with that of the vascular system as a whole.
The sinuses are as follows:
superior sagittal sinus (superior longitudinal sinus) extends from the
foramen caecum to the confluens sinuum (torcular Herophili). It lies
in the triangle formed by the inner layer of the dura mater as it tips
into the longitudinal sinus, and the outer layer of the dura as it remains
attached to the skull. This sinus receives the blood from the superior
cerebral veins, the diploe, the dura mater, and, in its posterior portion,
from the pericranial tissues.
inferior sagittal sinus (inferior longitudinal sinus) lies in the fold
made by the dipping dura as it is folded back upon itself at the inferior
or free edge of the falx cerebri. It terminates in the straight sinus.
It receives the veins of the falx cerebri, and sometimes a few from the
mesial surface of the brain.
straight sinus lies in the triangle formed by the two layers of the falx
and the tentorium cerebelli. It terminates at the confluens sinuum
occipital sinus lies in the angle of the attached margin of the falx cerebelli
as the superior sagittal sinus lies in the angle of the falx cerebri.
It communicates with the spinal veins and terminates in the confluens sinuum.
transvers sinuses arise from the confluens, and pass outward in the triangle
formed by the tentorial fold of the dura and the skull. At the base
of the petrous portion of the temporal bone the superior petrosal sinus
empties into the lateral sinus. It then communicates with the occipital
sinus, and unites with the inferior petrosal sinus to form the internal
cavernous sinus lies along the side of the sella tursica. It is a
continuation of the ophthalmic veins, and receives the blood of the spheno-parietal
sinus, a small sinus which follows the posterior border of the lesser wing
of the sphenoid bone. The right and left cavernous sinuses are joined
by the anterior and posterior sinus intercavernouses.
sinus terminates by dividing into the superior and the inferior petrosal sinuses.
The termination of the superior petrosal in the transverse sinus has already
been mentioned. The right and left inferior petrosal sinuses are joined
by the basilar plexus of veins, and unite with the lateral sinus to form the
internal jugular veins.